Implantable medical devices (IMDs) (e.g., pacemaker, neurostimulators, etc.) provide therapeutic stimulation to various tissues. IMDs include pace delivery circuits to control the amount of charge delivered to the tissue. Pace delivery circuits typically include a variety of components such as capacitors, switches, and batteries. One capacitor, connected to a battery, stores a charge that is applied to the heart muscle. Another capacitor, connected to an electric lead, prevents direct current (DC) from flowing through an interface between the lead and the heart muscle. DC currents degrade the ability of an electrical lead to stimulate the tissue. There are drawbacks to conventional pace delivery circuits. For example, each capacitor is physically large, which increases the size of the IMD.
Additionally, charge imbalance may occur during operation of the IMD. Charge imbalance degrades the ability of the IMD to produce effective tissue stimulation. For example, during pace delivery, the capacitor is partially discharged through the tissue load. Following this discharge, the capacitor is typically recharged with a current through the tissue load in a direction opposite to the direction of pace delivery. If the voltage across the capacitor is returned to a value substantially equal to a previous value, then generally no net current flows through the capacitor. If, however, the capacitor is recharged to a different voltage in preparation for delivering a pace pulse of a different amplitude, a net current may flow through the tissue load, creating an undesirable charge imbalance. It is desirable to have a device that overcomes the limitations associated with conventional pace delivery circuits.